This proposal contains plans for a detailed biochemical study of eukarytoic tRNA gene expression and its control. Using cloned yeast, Drosophila and vertebrate tRNA genes the work will focus on their detailed characterization, the elucidation of the DNa regions controlling transcription, the characterization of RNA polymerase III and of additional factors required for accurate tRNA gene transcription. Some of the enzymes involved in the conversion of the tRNA precursors to mature tRNA (e.g., processing nucleases, splicing enzymes, modification enzymes) will be purified and studied. The analysis of certain nonsense suppressor mutants of yeast will corroborate the biochemical results of this project.